The word on the street (and their website) is that Gamestop has dropped the price for The Dark Spire to $5. $5! I'm not sure there are any cheaper new DS games at that price, especially for a game that's only six months old. It's a pity it must've flopped so bad, but even the hardcore first person dungeon crawler community agreed that it wasn't so great.
Objectively speaking, the Etrian Odyssey games are both more modernized, less obtuse and way less buggy. But damned if I didn't really have an affection for The Dark Spire. I gave up somewhere after wandering around the second floor (and stumbling through the dark area in the basement), but the aesthetics are absolutely entrancing. There's something about the deeply saturated colors, the slightly off-skew angle, the bits of light peering in from the ceiling, and the enemy artwork that just clicks way, way more than Etrian Odyssey.
It also helps that the soundtrack is fantastic.
Maybe it's an effect of the Japanese industry dwindling, but the game music scene lately has felt a bit underwhelming, with most of the major players (Uematsu, Mitsuda, Sakimoto, Sakuraba) either mostly absent thsi year or past their prime. With Western development pushing the consoles forward, it's actually been the portable systems that have been picking up the slack with its outstanding music. The Dark Spire (along with Sting's Knights in the Knightmare) both sound like the composers sat down and had a healthy chat with Michiru Yamane - they both sound a bit like Castlevania - then each took off in their own direction. I've never heard of the composer, Kenichi Arakawa, but his VGMDB entry shows lots of obscurities. If he ever does anything else in the future, it'd be worth looking out for.
Like the heavy metal barking in the Shin Megami Tensei Nocturne soundtrack, it takes awhile to get used to the weird choir vocals in The Dark Spire, but everything - the main theme, the dungeon themes, all of the excellent battle themes - are outstanding, and definitely one of the best soundtracks released this year. For $5, the game comes in an outer cardboard box and includes a soundtrack CD that has most of the best songs, including a few of the "retro" variations, which are meant to sound like 8-bit chiptunes. Even if you have no interest in the game, it's worth it for the CD, and the cover looks cool anyway, assuming Gamestop hasn't banged it up or covered it with stickers per their usual MO.